Duplex communication



Feb. 21, 1928..

J. F. FARRINGTON DUPLEX COMMUNICATION Filed June 20. 1922 //1ve/1/ar.' John fi' Farr/779m. y z- 1/ M x t lug M 2 gs m Aff'y.

Patented Feb. 21, 1928'.

UITED STATES PATENT oFFica.

JOHN IE. FARRINGTON, OF NEVJ YORK, N. Y., ASSIGNOR TO WESTERN ELECTRIC COM- PANY, INCORPORATED, OF NEW YORK,

N. Y., A CORPORATION OF NEW YORK.

DUPLEX COMMUNICATION.

Application'filed June 20, 1922. semi No. 569,593.

This invention relates to carrier wave signaling circuits for two-way communication. An object of the invention is to provide improved methods and systems of duplexradio communication employing one antenna system, or two antennas systems placed so as to influence each other to a relatively large extent, whereby a conversation can be carried on between two persons at widely separated radio stations in the manner of ordinary telephone practice, that is, without the manipulation of any control or switch to change the circuit from talking to listening condition. Under certain conditions as for exampic, on board ship, the limited space available or other physical limitations'often necessitates the employment'of a single anten- 11a for transmission and reception. Under such circumstances the present invention may be advantageously applied, but it is not limited in application to systems employingv a single antenna for transmission and reception, but may be applied 1n systems where separate antennae are used.

duce a system which will facilitate two-way communicatlon over a system compr'lslng a telephone line connected to a radio system.

circuit or its equivalent is used in the receiv-' ing branch of the antenna when one antenna is used, and inthe receiving antenna when separate antennae are used for transmlsslon and reception to reduce the amount of locally transmitted energy transferred intov the receiving circuit. v In connection with the following detailed description reference is made to the accompanying drawings wherein Fig. 1 is a circuit diagram of a station for two-way radio telephony employing a single antenna and embodying the improvements of the present invention; Fig. 2 is a diagram illustrating a manner of connecting the system of Fig. 1 or any equivalent system to a two-way low A further object of the invention isto prodetector 12 of a conventional type.

frequency telephone line; and Fig. 3 is a circuit diagram of a system having separate transmitting and receiving antennae.

In Fig. 1 a microphone circuit 1 is connected to a transformer 2 of a radio transmltter 3 which is supplied with oscillations from a source 4:. These elements indicate in a conventional manner any known form of apparatus for producing high frequency waves and modulating them in accordance with speech for purposesof radio transmis-' sion, such, for example, as that described in U. S. Patent t0 Colpitt-s, et al., No. 1,388,450, grantedAugust 23,1921. The waves produced by the transmitter circuit are impressed upon the antenna circuit 5 which constitutes a suitable radiating aerial having a connectionjto ground through the coil 6 which serves as'a coupling coil. The antenna circuit has a branch path 7 which includes a loop resonant circuit 8 tuned to prevent waves of the outgoing frequency from traversing the path 7 The path 7 also includes a variable condenser 9 and a coil 10 in parallel which serve as tuning elements for the branch path 7. The coil 10 also serves to couple thebranchpath to the re ceiver circuit now to be described. The receiver circuit comprises a tuned circuit 11 coupled to the coil 10. The circuit 11 is included in the input circuit of a thermionic The circuit 11 is. a simple form of selective circuit for selecting the incoming hi h frequency. Greater selectivity maybe secured by using more complicated forms of selective circuits such as well-known types of band filters. The device 13 comprises a local source of waves of radio frequency which are supplied to the input circuit of the detector 12 by introducing them into the circuit 11. Sources 4 and 13 may conveniently be the type of vacuum tube oscillation generator described in U. S. 'Patent to Hartley No. 1,356,763, granted October 26, 1920, and capabl'e of having the frequency varied to any example, the oscillations may be different harmonics of a single base frequency from which they are. derived by. one or ,more harmonic producers, ofa WGllgdKIlQWIktYPG.

The essential characteristic of this selective circuit is that it must discriminate between Waves of different frequencies to the extent and in the manner hereinafter indicated. It may comprise any combination of elements necessary to accomplish this result. -Pre1"'er-- ably,--ho we er, iitis in-,;the fOllTlcOf a recur rent sectionalnetwork designedto pass av .band of frequencies:corresponding to the .auxiliary carrier and one or both ,-acc0n1-..:

loop circuit-Bis, adjusted to; prevents/too 11111011 energy of the outgoing rearrieixwave panyingside bands qvhichresult froin inodula-tion and to exclude all materially different I frequencies. -;Greater selectivity: may be secured by placinganother circuit similar to the circuit 15 between the-detector 12 and ...-the ilmpliiier- 14. The output terminals of circuit 15 are connected to a detector 16 avitlrwhich is associated a telephone receiver Y 4 17 or equivalent device.

Inoperation the person talking into the microphone or the circuit 1 and listening at the receiver l'Z-Will be enabled to communi- ,cateitha person at a distant-station. gThe incomingand outgoing carrienW-aves will preferably id'lfi eiyby an amount greaterithan the highest frequencies uof speech. .The

source 13Will produce undainpedi waves of such frequencythat they-Will combine With the incoming carni eraves; to produce a combination frequencywvave which can be separated from any combination frequency Waves produced lay-{the beating together of the incoming" and 'outgoing carrier Waves and any combination;frequencyvwave produced by -the modulated outgoingcarriX typical set-of frequency-values is: outgoing carrier frequency, 800,000;-:inco1ning carrier frequency 730,000 sou1';ce -13,'820,0O0;

difference ---frequen'cy --or ;auxi=li'ary carrier 90900; filhese are the frequenciesindicated on the dnavving. ,Many other combinations of frequencies might lie-used, thiusforqexample, outgoing carrier,"80 0,000; incoming carrier frequency 810,000; localsource 780,-

i000;- and ,auxiliary carrier frequency, "30,000 or 1,590,000. 'It'is an important considera ation that the present 'rnethod; permits the employment of outgoing and incomingcarr-ier ivavesldiifering from each Other 'in* frequency bye lative y ma lamou t, hi isoften desirjable. Good ,s'electiyity nequires, in the -,case-Where both ,the local and distant transmitters are transmitting both side; freque c of e r spectiv niodnlat d wav s,

{thatthe incoming and .ontgoing carrier aves; differ an amount at least twice the value of the highest frequencies which modulate the carnerwailes. lVith ordinary types of selective circuits a sornewhat greater fregreater than ten pefice'nt. .is& designed to pass the auxiliaryucarrier freq uencytogether with its vupper rorlower side band or both and to eXclude-wavesof Elements 9 and aresadjusted totune the whole antenna network t0.tl16T'1 I1COlTl1llg.:C&I' rier iv-aye frequency, :thus select1velyrece1vquencysepa *ation than-this is necessary but "xnunierousrconibinationsfof .Wave lengths may be utilized in which the frequency differ once is considerably lessmthancten per -cent not limited to cases of small frequency differcnce of the outgoing and incoming carrier Waves but may be advantageously employed \YllCiG the difference is considerably Thecircu'it other frequencies from the detectoriilti. :The 80 frequency from, traversing the branchopath '2' ant @hence-enterrng the receiving .:circu1t.

ingithe incoming Waves.

15V] th' sufficiently selective aclrcuits and proper shielding of the receiver:fronr thetransmitter a system such as described heren1 )5 an. anti-side tone-system 1. e.,= sounds impressed upon the microphone :of the circuit. 1 will notbe heardnin-the receiver: 117 Inpractice, however, some; side-tonejinay be present owing tothe fact:thatishielding and selectivity are notpe-rfect. designing the'systein so'that the side-toneis. reduced to a small volume as compared:tozthe-vol-unie of theiincoi'ninglsignal; true-duplex opera- 1 tion is available as distinguished from-atmomay systems wherein the .tlELIlSllllSSllQHfilIlithe two directions alternates.

' The present system iGZtIl be easily changed to operate in. accordance: with the method-.1

described; in applicarits-.-applicatio1r Serial @No 326,986,? filed September 1 27, "'1919,-:in

which the outgoing,andancoiningmaarier vwaves are combined to produce ahflnterrnediate frequency zoarrier Wave. r5l ordo-this .1

the generator 13 is stopped or disconnected from the input circuit;of j-detector 12,wand

Waves will freely pass .thru :the circniitxlfiito theidctector 16. The circuit 8; and

"the-elements 9 and 10 maynalso-need readni-stment. 1

Furthermore, the present systeinrwhenxuti- Q li-zing the :Wavesfrom the source ;13: may co-.

operate With a distantszstafion which operates to combine its 'lIlQO11'11Ilg"L;l1(1' outgoing carrier wavesto producezan au-Xili-a-rycar .125

rier- Wave of intermediate frequency. -lhns, let it be supposed that a. distant ico o rating station is similarin circuit-,arrangcinenj to the present station with the exceptions-that source 13 is omitted. The local station rafrequency waves from the output circuit of diates a carrier wave having a frequency of 800,000 cycles per second and the distant cooperating station radiates a wave having a frequency of 730,000 cycles per second. At the, distant station the outgoing and incoming carrier waves beat together to produce Fig. 2 illustrates the connection of a low frequency telephone line 18 to the system of Fig. 1 whereby a subscriber at the remote end of the line may communicate over the radiosystem. The line 18 is balanced by the balancing network N and is connected to the outputcircuit of the detector 16 and to the input circuit of the radio transmitter 3 by conjugately related paths 19 and 20. Path 19 transfers speech frequency waves incoming over the telephone line to the radio transmitter 3,-and path 20 conveys speech the device 16 to the line 18. The conjugate relation of connections 19 and 20 prevents local circulation of power or singing through the radio system. When a radio system is thus connected to a line 1t is desirable that V the side-tone in the radio circuit be as small as possible. 'This is an advantage of the present arrangement. It permits a high degree of suppression of side-tone.

Fig. 8 illustrates the application of the invention to a system employing separate antennae 6 and 7 for transmission and recept-ion respectively. These antennae may comprise aerial structures so closely related that they react strongly on each other. This would be the case for example, with two antennae mounted on the same vessel. They may, however, be moreremote from each other so that their mutual reaction will be less strong. The antenna 7 may be strongly directional so as to receive efficiently from the distant station, but inefficiently from the local transmitting antenna 6. The circuit 8 constitutes adjustable means for making the antenna circuit of high impedance to currents ofthe outgoing wave frequency. The elements 9, 10 function to tune the antenna 7 to resonance at the incoming wave frequency. The other elements of the system are of the same kind and function as described in connection with Fig. 1.

In all the arrangements described additional amplifiers may be introduced at any point in the system. Additional selective circuits may also be provided at any point in the system to discriminate against unclesired frequencies. Y V

Having described the invent-ion in detail the novel features believed to be inherent therein'are defined in the appended claims.

What is claimed is:

1. A two-way radio transmission s stem comprising an antenna, means for impressing a wave to be radiated on said antenna, a receiving circuit connected to said antenna, rejector means individual to the frequency of the outgoing wave for materially reducing the amount of energy of said wave which is impressed upon said receiving circuit, a local source of waves connected to said receiving circuit, means for combining waves from said local source with incoming carrier waves present in said receiving 01rcuitto produce waves of auxiliary carrier frequency, and means for deriving the signal currents to be received from said waves of auxiliary carrier frequency.

2. The method of duplex radio telephony by means of a single antenna structure serving. both for radiation and reception, comprising impressing outgoing carrier waves on said antenna structure, receiving incoming waves in said antenna structure, selecting said incoming waves to at least the part-ial exclusion of said outgoing waves, combining the incoming waves with waves from a local source to produce an auxiliary carrier wave having a frequency different from any frequency obtained by combining the incoming and outoging carrier waves, and selec ting and detecting said auxiliary carrier wave to reproduce the signal.

3. A radio transmission and reception circuit comprising a conductor system for radiating outgoing wave energy and absorbing incoming wave energy, a transmitting system for impressing carrierwaves 0f the given frequency to be radiated on said conductor system, a receiving circuit connected to said system, the connection including a circuit, anti-resonant to the radiated frequency, for allowing incoming waves to reach said receiving circuit while reducing the amount of energy of the radiated frequency supplied thereto, a locally controllable source of waves of a frequency other than saidradiated frequency, means for combining waves from said source with incoming waves to produce waves of an auxiliary carrier frequency, selective means for separating waves of said auxiliary carrier frequency from accompanying interfering waves, and means for deriving an incoming signal current from the separated waves.

4. A duplex transmission system comprising a source of waves to be transmitted, a radiating antenna comprising a path to ground coupled to said source, a branch path to ground, impedance means in said branch path ofiering highimpedance to waves of the frequency to be radiated, tuning means in said path for tuning said antenna system which are to be received, and means for coupling a receiver circuit to'said branch path.

5. A duplex transmission system compris= inga source of waves of one frequency to be radiated, a transmitting antenna comprising a path to: ground coupled to said source, a

branch path to ground includin impedance means for offering high impedance to Waves of the frequency to be radiated, tuning means in said path for tuning said antenna system as a whole to waves of a second frequency to be'received, means for coupling a receiver to said path and means for supplying to said receiver waves of a third frequency to COInb l-H-Wlth the receivedwavesto produce waves of a fourth frequencyhaving such a value as will allow their separation from waves of the first, second and third mentioned frequencies "orany troublesome combination frequency resulting therefrom.

16. The method of two-wayradio transmission by means of a single antenna-structure which comprises transmitting waves of one carrier frequency over said antenna structure, receiving incoming waves of another carrier frequency, combining waves of a third frequency with the incoming waves to produce waves of a fourth frequency which is sufliciently different from the sum or difference of the first and third mentioned frequencies to allow separation therefrom by selective circuits, and selecting and detecting said fourth frequ'encywave to reproduce the signal. 1

structure, selectively receiving waves of another carrier frequency over-said 7.The method of two way radio trans- I mission bymeans of a single antenna; structure which comprises transmitting waves of one carrier freop'iency over said antenna of either, combining waves ofa third frequency withthereceived incoming waves to produce waves ofa fourth frequency dlfiering from any frequency obtainedby'com-i bining the first frequency waves with the second-or third frequency waves, and selectmg and detecting the fourth frequency 'wave to reproduce the signal.

8. The method of two way radio transmission by means of a single antenna structure'which comprises transmitting waves of 0116ICEIFI'IGY'fIQQHQHCy' over said antenna incommg antenna, combining waves of athird frequency with the received waves to produce wavesof a fourth frequency which'is surficientl'y different from a frequency equal to the differences of the frequencies of the two first mentioned wave frequencies to allow" "separation "by selective circuits, and selecting and detecting said fourth frequency wave to =reproduce the signal. p 1

lnwitness' whereof, I hereunto subscrlbe my namethis19thday of June A. D., 1922.

JOHN F. FARRINGTON. 

